In orthopedic procedures it is common to use an acrylic bone cement to affix a prosthesis to the bone, for example a hip joint implant to the interior surfaces of the femur. Typically such bone cements are comprised of a liquid monomer and a solid polymer. The solid polymer contains the reaction initiator and is typically a finely divided powder. When the liquid monomer contacts the polymer, a reaction ensues that polymerizes the monomer and cross links the polymer into a high molecular weight polymeric solid. It is known that when the monomer and polymer are mixed under a partial vacuum, the void volume (portion of the volume occupied by air or other gas bubbles) of the resultant high molecular weight polymeric solid is advantageously considerably less than when mixed in air at atmospheric pressure.
Resulting bone cements of this type have been applied to the surgical site in a variety of ways. One way is to use an extrusion device broadly similar to a caulking gun. Typically in prior devices, the mixed bone cement is transferred to a cylindrical cartridge in air at atmospheric pressure or is mixed in the cartridge itself under a partial vacuum. Transfer of the cement into the cartridge in air at atmospheric pressure allows the incorporation of air into the mixture and thus unfortunately can increase the porosity of the cement. On the other hand, when the cement is mixed within the cartridge itself, the surface area available to remove the air from the mixture under partial vacuum is not optimal.
Accordingly, the objects and purposes of the present invention include provision of apparatus intended to overcome these and other drawbacks of prior systems.
A further object of the present invention is to provide adequate surface area to remove air during the mixing process and to transfer the mixed cement into the cartridge while under a partial vacuum.
One aspect of the invention involves an apparatus for mixing bone cement and containing the mixed bone cement preparatory to dispensing, the apparatus comprising a mixing chamber having an outlet for mixed cement, a cartridge having an inlet releasably coupled to the outlet of the mixing chamber for receiving mixed bone cement therefrom, and means for moving cement from an upper region of the mixing chamber down into a lower region thereof to mix same and for moving such mixed cement off an inner surface of the mixing chamber and into the cartridge.
Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following description and inspecting the accompanying drawings.